Some background for those concerned with inflation:
The US dollar is backed first and foremost by the global reserve status of our currency, which it became in 1971, as (probably the most important) part of the Bretton Woods System. As long as nations need US dollars to purchase crude oil, the US dollar will continue to be globally valuable.
Secondly, the US has a powerful military, including hundreds of essentially forward operating bases and air fields, lying in wait, all over the world.
Third, and as a secondary property of our military and economic strength, many countries are owed many billions of US dollars. This is because, due to the strength of the US military, T-bills (essentially bets made on the US dollar) are purchased by many nations. When other countries bet on the US dollar, they're creating a vested interest in the US dollar not collapsing, which increases the US leverage (leading to things like money printing).
None of this is meant to make you more too comfortable, because, despite all of the above, China, Russia, Libya, Iran, Brazil, South Africa, and, at times, India, have been attempting to reduce the US dollar hegemony by creating other means of trading oil.
For instance, Libya's late leader, Muammar Gaddafi, created a gold backed currency for trading oil (this is the reason NATO invaded Libya and killed Gaddafi). Russia and Iran made agreements to trade food (from Russia) for Oil (from Iran), which Russia would then add to its exports, acting as a trade proxy for Iran. This, combined with Iran's efforts to pipe natural gas and oil to China, is the reason for the supposed "Iranian nuclear threat". China has also recently created the Shanghai Gold Exchange, as a means to further commoditize fiat currency (china has very large gold reserves). BRICS has created a competitor to the Western-dominated IMF in the past 24 months, which also threatens the US reserve currency's backup plan, which is called the SDR (Special Drawing Rights). The list goes on; not to mention the calls Xi Jinping has directly made to remove the US dollar as a reserve currency (IOW, this isn't exactly covert, as of about mid 2010).
As you can see, considering our posturing in the South China Sea, and considering what happened to Gaddafi, the US won't acquiesce to losing its reserve status. So, the US dollar is not going to "collapse", lest we find ourselves engaged in total war (with China, et al). So, as long as you don't plan to bail on the US in a total war scenario, you're, in my opinion, safe to invest in USD.